Ultrasound and Microbubbles: Imaging Tumors and Delivering Drugs

Friday, November 20, 2020, 4:00 p.m.

Dr. Mike A. Averkiou
Department of Bioengineering
University of Washington
https://bioe.uw.edu/portfolio-items/mike-averkiou/

Over the last two decades, ultrasound imaging techniques based on nonlinear propagation and nonlinear scattering have been developed.  The first category gave birth to tissue harmonic imaging that helped reduce tissue aberration issues, and the second introduced contrast-enhanced ultrasound (CEUS) which enabled imaging of the tumor microcirculation with the help of microbubbles.  More recently, a new method of imaging that is referred to as “ultrafast” or plane wave imaging changed the transmit/receive beamforming paradigm and lead the way towards super resolution and real-time 3D imaging.  Also, investigations into ultrasound-mediated bubble dynamics led to a number of targeted tumor therapies such as sonoporation, vascular disruption, immunomodulation, and enhanced drug uptake.  This presentation will give a general overview of ultrasound imaging techniques based on nonlinear phenomena first, and then present clinical and pre-clinical examples.  Nonlinear propagation from complex plane apertures, nonlinear pulsing schemes, and passive detection of inertial cavitation will be discussed first.  Image-guided therapies for cancer based on ultrasound-driven microbubble phenomena will be presented next.  These include sonoporation, vascular disruption, drug delivery and bubble-enhanced heating.

The Sound of Spring Reverb

Friday, November 13, 2020, 4:00 p.m.

Dr. Kyle S. Spratt
Applied Research Laboratories
The University of Texas at Austin
https://www.arlut.utexas.edu/

A spring reverb is an electromechanical device used to artificially reverberate an audio signal, i.e. to impart a sense of spaciousness to the audio signal, as if the sound were being emitted into a reverberant acoustic space.  The device consists of a number of helical springs set into motion by electrically driven magnetized beads, with the elastic wave motion along the springs being analogous to acoustic waves propagating along the various dimensions of a room.  While originally invented by the Hammond organ company to add a sense of spaciousness to the sound of their electric organs, spring reverbs have been used in a number of electronic instruments and audio devices over the years, with probably the most iconic and enduring use being in classic electric guitar amplifiers.  In this talk a general overview of the history and technical aspects of spring reverb devices will be given, with particular emphasis placed on the highly dispersive nature of elastic wave propagation along helical springs, which it will be argued is primarily responsible for the distinctive sound of the device.  Finally, a simplified computation model will be presented that captures the salient features of a spring reverb device.

Wave Dynamics of Nonreciprocal Elastic Wave Metamaterials

Friday, November 6, 2020, 4:00 p.m.

Dr. Benjamin M. Goldsberry
Applied Research Laboratories
The University of Texas at Austin
https://www.arlut.utexas.edu/

Acoustic and elastic metamaterials with time- and space-dependent material properties have recently received significant attention as a means to violate the principle of reciprocity for wave propagation in acoustic and elastic media.  The creation of materials and systems that produce nonreciprocal wave propagation opens up the possibility for direction-dependent acoustic devices that may augment mechanical wave sensing and transmitting capabilities.  More generally, these materials may enable the creation of improved vibration isolation strategies for elastic structures.  This talk will review some of our recent efforts to numerically model linear nonreciprocal elastic wave propagation in metamaterials with time- and space-dependent material properties.  I will first introduce a finite element approach which is used to calculate direction-dependent frequency-wavenumber spectra of nonreciprocal metamaterials.  Examples of nonreciprocal elastic wave propagation in a honeycomb structure subjected to finite deformation will be presented.  I will then discuss a coupled-mode approach to model nonreciprocal vibrations of finite elastic structures.  The modulation parameter space is explored for designs that yield a large degree of nonreciprocity for low-frequency longitudinal and transverse vibrations.  This talk will conclude with a brief discussion on potential avenues of future research.

Understanding Naturalistic Speech Processing Using Invasive and Noninvasive Electrophysiology

Friday, October 30, 2020, 4:00 p.m.

Professor Liberty S. Hamilton
Department of Speech, Language, and Hearing Sciences
The University of Texas at Austin
https://slhs.utexas.edu/research/hamilton-lab

Understanding natural speech involves parsing complex acoustic cues from multiple sources in order to create meaningful percepts.  Our work uses encoding models to understand how the brain extracts phonological and acoustic information from naturalistic speech stimuli, using a combination of intracranial electrophysiology in patients undergoing surgical treatment for epilepsy and scalp EEG in non-patient participants.  This talk will describe efforts to extend encoding models to continuous speech from highly dynamic, noisy, audiovisual stimuli.  The overall goal is to understand the transformation of acoustic to linguistic information in the brain, which could help with the development of brain computer interfaces for speech as well as brain-based treatments for hearing and communication disorders.

Super-resolution Ultrasound Imaging Beyond the Acoustic Diffraction Limit

Friday, October 23, 2020, 4:00 p.m.

Professor Kang Kim
Department of Bioengineering
University of Pittsburgh
http://www.pitt.edu/~kangkim/

Ultrasound imaging is one of the most favored imaging modalities in clinics in general because of its real-time display, safety, noninvasiveness, portability, and affordability.  One major disadvantage of ultrasound imaging is its limited spatial resolution, which is fundamentally governed by the acoustic diffraction limit of the operating ultrasound.  A recent development of super-resolution imaging can achieve unprecedented high-spatial resolution beyond such limitation.  The concept of super resolution that bypasses a physical limit for the maximum resolution of traditional optical imaging was originally introduced in the microscopy imaging community and later developed into a ground-breaking technology of the nano-dimension microscopy imaging, for which the Nobel Prize in Chemistry was awarded in 2014.  In brief, microscopy super resolution imaging technology is based on the randomly repeated blinking process of fluorophores in response to the light source of the microscopy.  In recent years, the concept has been translated into the ultrasound imaging community.  The random blinking process that is required for achieving super resolution using ultrasound is provided by flowing microbubbles in blood vessels which randomly oscillate in response to the ultrasound pressure from the imaging transducer.  The maximum spatial resolution in super resolution microscopy technology is in the range of tens of nanometers, which allows to visualize the pathways of individual molecules inside living cells, while ultrasound super resolution imaging can achieve a spatial resolution in the range of tens of micrometers when using a typical clinical ultrasound imaging transducer of a few MHz center frequency.  Due to the large imaging depth of ultrasound of up to several centimeters, ultrasound super resolution imaging technology is practically very useful in imaging human subjects with greater detail of microvasculature, which is of critical importance for many diseases.  In this talk, I will introduce super resolution ultrasound imaging algorithms and discuss their advantages and limitations in some applications to diseases, including identifying vasa vasorum in atherosclerotic plaques and assessing microvessel rarefaction in the progress of acute kidney injury to chronic kidney disease.

Gradient-based Optimization for Structural Isolation and Acoustic Scattering Minimization

Friday, October 16, 2020, 4:00 p.m.

Dr. Benjamin C. Treweek
Sandia National Laboratories
Albuquerque, New Mexico
https://www.sandia.gov/

Acoustic and elastic metamaterials have shown potential for many different applications in wave manipulation and structural isolation.  To this end, a wide variety of designs have been proposed, many of which are difficult to manufacture or involve large numbers of tunable parameters.  In the latter case, the design parameter space quickly becomes prohibitively large for optimization strategies based on global searches, raising the need for gradient-based methods to make problems computationally tractable.  This talk will include a basic description of PDE-constrained optimization and inverse methods in Sierra/SD, a massively parallel implementation of the finite-element method applied to structural dynamics.  Several examples of gradient-based optimization will then be presented, including a split-ring resonator for vibration isolation and two separate designs for minimizing a scattered pressure field via optimized material distributions in an annulus surrounding a rigid scatterer.  Optimized designs will be shown for one or more excitation frequencies.  The talk will conclude with a brief discussion of future research possibilities.

Scary Memories of the Cold War, Huge Thermonuclear Explosions, and Unraveling the Physics of Shots Heard Around the World

Friday, October 9, 2020, 4:00 p.m.

Professor Emeritus Allan D. Pierce
Department of Mechanical Engineering
Boston University
Career in Acoustics

At the height of the Cold War, the US and the USSR during 1954 to 1962 exploded a number of thermonuclear devices in the atmosphere.  Energy releases of these devices were of the order of the equivalent of 10 megatons of TNT (1 MT = 4.194 petajoules).   The explosions generated pressure pulses that traveled very large distances, and which were often observed to travel around the world.  Because the pulses were composed of extremely low infrasonic frequencies, with periods of the order of minutes, the physics heavily involved the earth’s gravity, and the customary formulations of atmospheric acoustics were not applicable.  The physics had some subtleties which were not immediately understood.   Source modeling required understanding that nuclear bombs added energy, not mass, to the atmosphere.  Also, the ducting of the pulse included a hitherto misunderstood guided mode, where gravity held acoustic energy to the lower regions of the atmosphere.  Ideally, the R&D community wanted to work back from recordings of the pulses to estimate the energy released by the explosions.  This was complicated by the global variability of atmospheric temperature and wind profiles.  The concept of horizontal refraction emerged during the study and it was found that the initial portions of the waveforms were guided by the near-surface mode.  An approximate theory was developed whereby the energy could be estimated from a simple formula involving the observable features of the first few cycles of the waveform. (Nature, Vol. 232, July 23, p. 253, 1971.)

Acoustic Radiation Forces and Torques for Extraordinary Manipulations of Particles

Friday, October 2, 2020, 4:00 p.m.

Professor Likun Zhang
National Center for Physical Acoustics
and
Department of Physics and Astronomy
University of Mississippi
https://physics.olemiss.edu/zhang/

Acoustic waves, analogous to optical waves, can transfer linear momentum and angular momentum to illuminated objects, and hence exert radiation forces and torques on the objects.  Manipulations of objects using radiation forces and torques produced by acoustic waves have led to the development of acoustic tweezers and relevant non-contact manipulation techniques for valuable applications in biomedical and material engineering.  This talk will review some of our recent research on physics and experiments of acoustic radiation forces and torques for extraordinary manipulations of particles.  The physics and manipulations include uses of non-diffracting sound beams as acoustic tractor beams to pull objects towards the sound sources, control of beam paraxiality to advance flexibility of particle trapping, formulization of three-dimensional radiation forces using scattering phase shifts to gain insight, relating radiation torque exerted by orthogonal standing waves to viscous absorption, viscous radiation torque generated by vortex beams with a screw phase dislocation, and forces and torques exerted by these relevant beams on acoustic interfaces.

Mechanical Tissue Ablation Approaches in Therapeutic Ultrasound

Friday, September 25, 2020, 4:00 p.m.

Dr. Tatiana D. Khokhlova
Department of Medicine
University of Washington
https://gastro.uw.edu/faculty/tatiana-khokhlova-phd

High Intensity Focused Ultrasound (HIFU) therapy is a non-invasive medical technology in which an ultrasound beam is focused within the body to locally ablate the targeted site without damaging intervening tissues.  The most common (and currently clinically adopted) HIFU treatments rely on thermal ablation.  Histotripsy is a more recent HIFU-based technology in which the targeted tissue is fractionated down to subcellular level, i.e. ablated mechanically, via controlled cavitation.  Short (microseconds to milliseconds) bursts of high amplitude HIFU waves are delivered at a low duty cycle to induce gas and/or vapor bubble activity at the transducer focus which disintegrates tissue.  Multiple histotripsy approaches have been proposed and implemented over the years, including shock-scattering histotripsy, boiling histotripsy, and microtripsy.  The approaches differ in the specific physical mechanisms that lead to the generation of bubbles and tissue disintegration, and imply different HIFU exposure parameters and requirements to transducers and instrumentation.  This talk will review the mechanisms underlying different histotripsy approaches, instrumentation design, image guidance methods, preclinical studies, and clinical applications of the histotripsy approaches.

Psychoacoustic Implications of the Dynamic Vocal Tract

Friday, September 18, 2020, 4:00 p.m.

Erik K. Landry
Vocodojo Voice Center
Austin, Texas
http://www.vocodojovoicecenter.com/ 

Voice is the product of complex biomechanical and aerodynamic events.  During connected speech, the bioacoustic energy of the voice is processed by the listener at the subconscious level, conveying information such as the individual’s gender, their health, their age, and their emotional state.  But without a series of dynamic resonating chambers to contour, dampen, and augment the acoustic energy, the voice quality of an individual would be less robust with information.  This talk will go over the physiological subsystems of the human voice, focusing on vocal tract configurations and their psychoacoustic implications.

Biomedical Applications for Ultrasound-triggered Exploding Nanodroplets

Friday, September 11, 2020, 4:00 p.m.

Professor Tyrone M. Porter
Department of Biomedical Engineering
The University of Texas at Austin
https://www.bme.utexas.edu/people/faculty-directory/porter

Ultrasound can be used to noninvasively vary the pressure within tissue by several atmospheres.  The design of particles that respond specifically to these pressure variations is an active area of research within biomedical ultrasound.  In this talk, I will discuss the development and utility of pressure-sensitive nanoemulsions that can be vaporized with high-amplitude acoustic pulses.  The bubbles produced by vaporization can be driven to collapse, radiating broadband emissions that are rapidly absorbed by surrounding tissues and generate stresses sufficient for transient permeabilization of cells.  In one project, we demonstrate that vaporizable nanoemulsions can be used to facilitate transport of biomolecules into cells efficiently and with minimal cell death.  In a second project, we show that it is possible to dramatically reduce the acoustic power and exposure time required for tumor ablation using vaporizable nanoemulsions.  Recently, we have utilized the combination of nanodroplets and ultrasound for focal ablation in the brain.  Finally, new innovations for targeted imaging and localized therapy based upon the current research will be discussed.

Wave Propagation in Nonlinear Elastic Metamaterials

Friday, September 4, 2020, 4:00 p.m.

Dr. Samuel P. Wallen
Applied Research Laboratories
Walker Department of Mechanical Engineering
The University of Texas at Austin
https://www.arlut.utexas.edu/

Metamaterials (MM) have become a very active topic for research in numerous domains of engineering and science because of their promise to create materials, structures, and devices that can control wave propagation in ways that exceed the capabilities of conventional homogeneous and composite materials.  Most acoustic and elastic MM research has been focused on linear behavior.  However, linear MM suffer from a few notable drawbacks, such as a) the effective material properties of interest tend to be limited to narrow frequency bands that cannot be changed by external stimuli, and b) they have very limited usefulness in applications where nonlinearity is unavoidable or essential, e.g., shock testing or high-intensity focused ultrasound.  Nonlinearity has therefore been explored as a means to expand the palette of accessible dynamic response of synthetic materials to external stimuli.  Examples of desirable behavior include increased bandwidth of specific performance criteria by creating tunable band gaps via material configurability, enhanced harmonic generation, and improved control over the magnitude and shape of propagating elastic waves.  This talk provides an overview of linear and nonlinear acoustic and elastic MM, including historical context of metamaterials and composite materials; presents results from recent nonlinear MM projects at UT Austin on the topics of non-reciprocity, pulse shaping, and two-dimensional solitary waves; and will finish by discussing promising avenues of future research.

Finite Element Models of Acoustic Scattering from Elastic Targets in Seafloor Environments

Friday, May 1, 2020, 4:00 p.m.

Dr. Aaron Gunderson
Applied Research Laboratories
The University of Texas at Austin
https://www.arlut.utexas.edu/

Finite element models are ideal for solving underwater acoustic scattering problems due to their high accuracy and ability to capture scattering effects from environmental complexity, such as seafloor layering, clutter, bathymetry, and interface roughness, and object burial. In particular, three-dimensional models are known to break the symmetry constraints of the more commonly used two-dimensional models, but require significant computation time and processing overhead. This work will investigate techniques for 3D modeling which facilitate evaluation of large-scale 3D scattering solutions from elastic targets in complicated ocean environments. A numerical Green’s function determination method is demonstrated to permit model solution over very small physical domains, extending just beyond the target edges. By determining the Green’s function numerically within the model, analytic forms of Green’s functions for complex ocean environments need not be known or estimated ahead of time. This work also explores the use of nontraditional scattering formulations, Floquet-Bloch periodicity, and tapered plane wave approaches to simplifying the target scattering and increasing numerical predictive accuracy in the context of target scattering in seafloor environments. Together, these techniques permit highly accurate solutions of scattering within arbitrary complex environments, and have generalizability to a number of environmental contexts.

Multimodal Cues in an Anuran Courtship Display

Friday, April 24, 2020, 4:00 p.m.

Dr. Logan S. James
Department of Integrative Biology
The University of Texas at Austin
https://integrativebio.utexas.edu/

Communication systems involve a variety of cues, which may facilitate detection and decision-making. For example, female túngara frogs and frog-eating bats generally rely on acoustic cues produced by males for mating or foraging, respectively. However, the acoustic signal is accompanied by other cues, including the inflation of the male’s vocal sac and ripples created in the water by that motion, and both cues have been shown to affect detection and decision-making. To date, we do not know the natural variation and covariation of these three signal components. To address this, we made detailed recordings of male túngara frog calls, including call acoustic properties, vocal sac size and ripple height across many individuals. We correlated these features to understand the degree of information overlap, as well as identify which feature(s) predicted body size (a trait of interest to both receivers). In this seminar, I will present preliminary results on the relationships among multimodal aspects of a communication system, as well as propose future studies using these results to understand how receivers integrate and compare simultaneous information streams.

Nonlinear Effects on Tonal Sound in Lined Ducts

Friday, April 3, 2020, 4:00 p.m.

David A. Nelson
Nelson Acoustics
Elgin, Texas
https://nelsonacoustical.com/

Porous sound absorbers in various forms have long been a familiar part of the noise control palette. NASA researchers sought to extend their use to jet engine inlet duct liners in the 1970s, but discovered that the liners underperformed in flight relative to experiments on the ground. Mass and geometric constraints prevented the designs from simply being scaled up to recover lost performance. A nonlinear effect was suspected because of the finite sound amplitudes involved. This was eventually confirmed through carefully controlled experiments. The latter exhibited strange phenomena, at variance with “normal” nonlinear acoustics, suggesting that the designs could not be optimized without first mastering the physics. A NASA research grant to ARL:UT underwrote one Ph.D. and one master’s thesis, through which the mystery was finally solved. This lecture will describe the physics of porous sound absorbers and the nonlinear mechanism controlling their behavior at finite amplitude, along with application to lined ducts in linear and nonlinear regimes.

Understanding and Simplifying Complex Acoustic Data for Longterm Autonomous Monitoring

Friday, February 28, 2020
4:00 p.m. in ETC 2.136

Brennan Dubuc
Department of Civil, Architectural and Environmental Engineering
The University of Texas at Austin
http://www.caee.utexas.edu/

Nowadays, monitoring structural damage evolution and understanding its longterm impact is crucial. With acoustic-based methods being some of the most promising for autonomous monitoring purposes, this research centers on advancing these methods for reliable longterm applications in a range of critical structures. The goal is to characterize damage in its early stages and over time, so that decision-making and remedial measures can be strategized. Acoustic methods offer unique strengths in this area due to their non-invasive nature, versatility, and high sensitivities to important damage characteristics. Such sensitivities, however, also pose a challenge. Accounting for extraneous sensitivities is one of the forefront missions within the broad field of structural health monitoring. This research therefore targets this challenge to unlock the full potential of acoustic methods. With complex and potentially large acoustic data, the aim is to discover methods of data simplification via theoretical insight, as well as techniques for grappling with and understanding the data when simplification is not feasible. Case studies are presented across a range of structures and components, including prestressing/post-tensioning strands, prestressed concrete, and aircraft fuselages.

Stories in Spatial Audio

Friday, February 21, 2020
4:00 p.m. in ETC 2.136

Dr. Anne Guthrie
Arup
San Francisco, California
https://www.arup.com

In the past few years, we have seen a proliferation of affordable recording devices and playback systems as well as widely-accessible platforms for spatial audio. Arup’s acoustics and AV team has been on the forefront of spatial audio technology since 2000 and continue to utilize a variety of spatial audio systems as both design tools and desired project outcomes. As a sound artist, a researcher and as a consultant at Arup, the presenter has encountered many unique challenges and benefits of this oft-neglected layer of psychoacoustic experience within the built environment. The presentation will begin with a brief overview of spatial audio technologies and theory, followed by case studies from the presenter’s sound art, PhD work and Arup projects.

Underwater Acoustic Measurements of the Construction and Operation of the Block Island Wind Farm

Monday, February 10, 2020
4:00 p.m. in ETC 2.136

Professor James H. Miller
Ocean Engineering and Oceanography
University of Rhode Island, Narragansett, Rhode Island
https://web.uri.edu/oce

The Block Island Wind Farm (BIWF), the first offshore wind farm in the US, consists of five 6-MW turbines 3 miles southeast of Block Island, Rhode Island in water depths of approximately 30 m. Construction began in the summer of 2015 and power production began in late 2016. Underwater acoustic and geophysical measurement systems were deployed to acquire real-time observations of the construction and initial operation of a wind facility to aid the evaluation of environmental effects of future facilities. The substructure for these BIWF turbines consists of jacket type construction with piles driven to the bottom to pin the structure to the seabed. The equipment used to monitor construction and initial operation consisted of a towed array consisting of eight hydrophones, two fixed moorings with four hydrophones each and a fixed sensor package for measuring particle velocity. This sensor package consists of a three-axis geophone on the seabed and a tetrahedral array of four low sensitivity hydrophones at 1 m above the bottom. Data collected on these sensor systems during construction and initial operation will be summarized. Measurements of pile driving noise are compared to finite element models. Operational noise is compared to a ray-based air-water model using of the turbine blade kinematics.

Immersive Experimentation: Pushing the Boundaries of Acoustic and Elastic Wave Experiments

Wednesday, February 5, 2020
2:00 p.m. in CPE 2.218

Dr. Dirk-Jan van Manen
Department of Earth Sciences
ETH Zürich
Switzerland
https://eeg.ethz.ch/

Wave physics is traditionally investigated with complementary experimental and numerical approaches. Whereas numerical simulations provide the foundation for hypothesis testing of modeled physical relationships, laboratory experimentation can be used to explore novel physics. In immersive experimentation this complementary, two-pronged approach is replaced in favor of a hybrid investigation approach, which integrates physical and numerical wave experimentation through special immersive boundary conditions (IBCs). Virtual media with modeled or measured physical relations can be linked to any physical medium that may be governed by different or unknown physics. Real-time immersion, as enabled by a low-latency control system connecting hundreds of transducers surrounding the medium, allows waves to propagate seamlessly between the physical and the virtual medium, removing boundary reflections while correctly producing all wavefield interactions. This makes it possible to investigate wave phenomena that were previously inaccessible experimentally, and to perform experimentation at lower frequencies. In this talk, we will show examples of the 1-D and 2-D implementations, but focus on the practical aspects of the 3-D underwater implementation, including on a bespoke system capable of extrapolating wavefield values from 800 sensors to 800 boundary sources (and through the desired numerical environment) for up to 250 time-steps into the future, with a 200μs latency. Custom sources and sensors developed in close collaboration with the Walker Department of Mechanical Engineering will also be discussed. The ability to impose arbitrary IBCs on an experimentation domain has many applications. In one example, we convert a 2-D circular acoustic waveguide into a larger physico-virtual square waveguide that includes a non-physical energy-gain material, in real-time. In another example, we show how IBCs can be used to experimentally realize novel phononic and parity-time symmetric materials.

The Acoustic Monitoring of Climate Change

Friday, January 31, 2020
4:00 p.m. in ETC 2.136

Dr. Gabriel R. Venegas
Applied Research Laboratories
The University of Texas at Austin
https://www.arlut.utexas.edu/

Global CO₂ concentrations are higher than they have been in the last 800,000 years (Luthi et al., 2008) and continue to rise, leading to what is thought to be the fastest increase in ocean acidity in the last 60 million years (Turley and Gattuso, 2012). The increase in greenhouse gasses in the atmosphere warms the planet and its oceans, which decreases the solubility of CO₂ in the ocean and instigates a positive feedback loop. As a result, glaciers and polar icecaps are melting, extreme weather patterns are occurring, and the existence of valuable ecosystems that store up to half of the seabed’s rich carbon reserves are being threatened.  With economic incentives to protect these ecosystems, i.e. carbon budgeting, precise and rapid monitoring of sediment organic carbon content is of vital importance. First, we will showcase the work of some of the many acoustical oceanographers that have made valuable contributions to help monitor climate change from below the ocean’s surface. Then, we will take a deep dive into the motivation and development of an ultrasonic sediment probe to rapidly predict sediment organic carbon in situ.